The present invention relates to a fuel injector.
A fuel injector having a valve-closure member which is attached to a valve needle and which cooperates with a valve-seat surface formed on a valve seat member to form a sealing seat is described in U.S. Pat. No. 4,766,405. Electromagnetic actuation of the fuel injector is provided by a magnetic coil, which cooperates with an armature which is connected in a force-locking manner to the valve needle. An additional cylinder-shaped ground is arranged around the armature and the valve needle, and is connected to the armature via an elastomer film.
The disadvantage of this arrangement is particularly the complicated construction, requiring an additional component. The large-surface elastomer ring also interferes with the shape of the magnetic field and makes closure of the electric flux lines difficult, so that it is also impossible to achieve high starting forces in the opening movement of the fuel injector.
Another embodiment is described in U.S. Pat. No. 4,766,405 in which an additional cylindrical ground is provided around the valve needle and the armature for damping and debouncing, and which is movably secured in position by two elastomer rings. When the valve needle comes into contact with the sealing seat, this second ground is able to move relative to the armature and valve needle, thus preventing bouncing.
The disadvantage of this embodiment is the additional complexity and space requirement. Moreover, the armature itself is not decoupled, and the impulse therefrom increases the tendency of the valve needle to bounce.
A fuel injector is described in U.S. Pat. No. 5,299,776 having a valve needle and an armature, in which the armature is movably guided on the valve needle, and whose movement in the direction of the valve needle""s lift is limited by a first stop, and in the opposite direction by a second stop. The axial travel of the armature thus defined by the two stops causes decoupling to a limited extent of the valve needle""s inert mass from the armature""s inert mass. This in some degree counteracts the tendency of the valve needle to rebound from the valve-seat surface when the fuel injector closes. However, since the axial position of the armature relative to the valve needle is entirely undefined because of the armature""s free mobility relative to the valve needle, bouncing is only prevented to a limited degree. In particular, the fuel injector construction described in U.S. Pat. No. 5,299,776 does not prevent the armature from coming into contact with the stop facing the valve-closure member when the fuel injector closes, and thereby abruptly transferring an impulse to the valve needle. This abrupt impulse may cause additional bouncing of the valve-closure member.
It is also known from actual operation to use an elastomer ring to movably fasten in position the armature which is movably arranged on the valve needle. For this purpose, the armature is restrained between two stops, an elastomer ring being arranged between the armature and the bottom stop. However, this presents the problem that a hole must be provided through the armature to allow the fuel to reach the valve-seat surface. The hole through the armature is provided close to the valve needle.
The fuel injector according to the present invention has the advantage over the related art due to the fact that, by their position and structure, the intermediate rings situated between the armature and the damping element, and/or between the damping element and the flange assure balanced pressure conditions, so that the damping element remains securely in place and cannot be damaged by slipping. The radially and/or axially extending channels assure fluid equalization between an interior volume delimited by the valve needle, the armature, and the damping element on the one hand and a central cutaway in the fuel injector on the other. Fluid equalization provides additional damping according to the principle of a shock absorber.
In addition, the damping element is supported by the intermediate rings, thereby preventing the elastomer ring from vibrating.
The drainage holes in the flange may be produced simply and drain the fuel between damping element and valve needle away rapidly and without turbulence.
The intermediate rings are advantageously furnished with grooves that extend radially outward, e.g., in the form of an embossed structure, so that the fuel on the lower and upper side of the damping element may also be removed. In this way, not only is an overpressure and thereby lateral slippage of the damping element avoided, but also the bouncing behavior of armature and valve needle is positively influenced, since the viscosity of the fuel enhances the damping effect, and thus counteracts the bouncing.
The gap between valve needle and armature may be drained in a particularly simple manner by segment welding in such manner that the valve needle is joined to the flange not by an uninterrupted weld seam, but by spot welding, whereby sections of attachment alternate with passages through which the fuel may flow.
A combination of the individual drainage devices is particularly advantageous, so that for example the flange may be connected to the valve needle by segment welding and the damping element has intermediate rings on the inlet and the outlet sides.